Mountain Weather Forecast

Time and Day: 0630 Friday

The Snapshot:  Light snow today, possibly light rain on the lower mountain this evening. Light snow Saturday morning becoming heavy Saturday night with significant cooling. 

 

The Science: Temperatures have gradually risen overnight as warm air advects into Western Washington. Satellite imagery shows a triple point frontal system centered a few hundred  miles offshore. High clouds ahead of the warm front have spread over much of the state, and the edge of the warm front is just reaching the coast. It should cross the Cascade crest midday, with the warmest air filling in behind. The precipitation should begin as snow today, with light to moderate amounts. The highest probability for rain on the lower mountain will be when the warmest airmass crosses the crest, between the warm and cold front, between 4pm and 10pm. Late this evening/early Saturday morning cold air will fill in behind the cold front, lowering snow levels. Precipitation will also taper off but Stevens Pass will likely see light snow showers very early Saturday morning.

Saturday will be cooler with gusty winds. Snow flurries in the morning will increase to light showers midday, and finally pick up in earnest Saturday afternoon. Strong zonal (upper level due westerly) flow will provide orographic lift producing heavy snow into Sunday morning. A large, very cold, Arctic airmass will sag south out of British Columbia Saturday evening bringing the coldest temperatures of this season.

 

The Long Range: Precipitation will end Sunday morning for a brief break. Much of the Pacific Northwest will be under cold, northerly flow Monday and Tuesday with Arctic air sagging all the way into Oregon. Stevens Pass will see temperatures in the low teens and light precip amounts. There is a possibility of lowland snow in the Puget Sound area Monday night.

 

 

Precipitation Ending at 4am:

 

Today 24hr water = .5"   Snow = 3" in base area   4-6" on upper mountain

 

Tomorrow’s 24hr water = 1-1.25"     Snow = 12-14"

 

Trend and Timing:
Light snow during the day Friday, possibly switching to light rain below 4500' in the evening. Light snow early Saturday, becoming moderate during the day and heavy overnight into Sunday morning.

 

24hr temperature ending at 4 am tomorrow: 

                                     

Low:  26   High: 34

Freezing level: 4,500-3,000

 

Trend and Timing:   

Temperatures will continue to rise throughout the day, peaking in the late afternoon/evening, then rapidly cooling after midnight. 

  

24hr Winds (mph) ending at 4 am tomorrow:

Base: W 0-5, then W 10-15

Ridge Top: SW 20 then W 20-30

 

Trend and Timing:

Ridgetop winds should strengthen from the SW throughout the day, then switch to due westerly and become gusty this afternoon with the cold front passage.

DV